This invention relates to a binder-less porous donor for producing a dye diffusion thermal transfer image.
A dye diffusion thermal transfer system is broadly used because it can produce an image in a completely dry process with a non-impact system using digitalized image information, the produced image having a high continuous gradation. In this system, image formation has hitherto been carried out by bringing a donor layer comprised of dyes and a macromolecular binder fixed on a donor substrate film in contact with a receptor layer on which an image is to be formed, bringing a thermal head into contact with the surface of the donor substrate film opposite the surface on which donor layer is placed, diffusing the dyes in the donor layer onto the receptor layer perpendicularly to the surface of the receptor layer by the thermal energy supplied from the thermal head, and then fixing the dyes thereon. This system is schematically illustrated in FIG. 1.
Such systems are disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) Nos. 3-13386, 3-65394, 3-65395, and 3-86589. In conventional films using binders, a high affinity between the dyes and the binder is required in order to sufficiently diffuse the dyes in the donor layer. If the affinity is high, a high thermal energy is required for diffusing the dyes into the receptor layer. An energy threshold of diffusion of the dyes also exists. Thus, it is difficult to form an image having both a high continuous gradation and a high optical density at a low thermal energy.